What Causes Eosinophilia?

Eosinophilia is classified as primary or secondary, in addition to the hypereosinophilic syndromes.

Primary Eosinophilia

Primary eosinophilia is a rise in the peripheral eosinophil count without any underlying condition to account for it. It is subclassified into clonal and idiopathic types.

Clonal primary eosinophilia is the type of eosinophilia that is due to proliferation of a clone of eosinophils in the bone marrow, and is found in leukemias or other myeloproliferative disorders.

Idiopathic primary eosinophilia is a term used to refer to peripheral blood eosinophilia without any detectable cause.

Secondary Eosinophilia

Secondary eosinophilia is the result of other disorders not associated with bone marrow proliferation, such as atopy, asthma, and most commonly helminthic infestations.

Hypereosinophilic Syndromes

Hypereosinophilic syndromes are disorders which are characterized by eosinophilia above 1500/µL persisting for at least 6 months, with no underlying disease condition, but associated with organ dysfunction due to eosinophil recruitment into tissues which suffer resulting damage. These include the syndromes of pulmonary eosinophilic infiltrate with eosinophilia, such as:

Churg-Strauss syndrome

Tropical pulmonary eosinophilia

Etiology of Secondary Eosinophilia

The following simple classification may help to understand the manifold conditions which may give rise to secondary eosinophilia.

Allergic conditions, especially of the skin and the respiratory tract, such as;

atopic dermatitis

asthma

bronchopulmonary aspergillosis

allergic rhinitis

non-allergic rhinitis with eosinophilia syndrome (NARES)

occupational pneumoconiosis

urticaria

milk protein allergy

Connective tissue disorders such as;

Dressler syndrome

Eosinophilic fasciitis

Inflammatory bowel syndrome

Sarcoidosis

Rheumatoid arthritis

Systemic lupus erythematosus

Polyarteritisnodosa

Immune disorders such as;

Graft-versus-host disease

Congenital immunodeficiency syndromes such as Wiskott-Aldrich syndrome or IgA deficiency

Certain tumors, such as Hodgkin’s disease, also result in eosinophilia. Others include

Acute or chronic eosinophilic leukemia

Some types of acute lymphoblastic leukemia

Chronic myelocytic leukemia

Invasive parasite infestations result in a rise in the number of peripheral blood eosinophils, such as

Ascariasis (tapeworm infestation)

Echinococcosis (dog tapeworm infestation)

Filariasis

Cysticercosis

Hookworm

Visceral larva migrans

Schistosomiasis (liver fluke infection)

With regard to parasitosis, a sustained rise in eosinophils is usually seen when the parasites migrate into tissues and come into contact with patrolling immune cells. Once the parasite is walled off within a cyst, or is dormant, eosinophilia tends to fade. Only if the cyst leaks and parasite products again become exposed to immune effector cells (T-lymphocytes) does eosinophilia again appear. Parasites which remain within the lumen of the gut during their whole lifecycle rarely cause persistent eosinophilia.

Again, protozoal infection is not usually a cause of a raised eosinophil count. However, ectoparasites such as the scabies mite are associated with eosinophilia.

Further Reading

Liji Thomas is an OB-GYN, who graduated as gold medallist from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.

In this interview, AZoNetwork speaks to Knauer about the use of FPLC for purification of proteins and
how their products enable scientists to get the most of liquid chromatography; conducted by Matthew Rafferty

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